No Low RPM power steering on 99 Plym Grand Vouager

I just replaced the power steering pump for the second time. Problem is there is no power steering at low RPM. Once it hits about 1500 RPM it works fine. I followed the procedure for bleeding the system and it has plenty of fluid. New Pully and belt seems fine. My blessed son ran it for a few days with no fluid until it seized.

Sounds like a possible problem in the rack, bad seals not allowing pressure to be built perhaps. That is of course assuming that the belt is not slipping.